Jar



2 Sheets-Sheet 1 JOHN 7.' ,DH/pps 5%@ ATToRN J. T. PHIPPS JAR Filed May 27, 1940 Elm 32 July 1, 1941.

J. T. PHIPPS July l, 1941.

JAR

Filed May 27, 1940 2 Sheets-Sheet 2 INVENTOR Jo//A/ 7.' P14/MP5 TTORNEY Patented July 1, 1941 JAR John T. Phipps, Huntington Park, Calif., assigner to S. R. Bowen Co., Huntington Park, Calif., a corporation of California Application May 27, 1940, Serial No. 337,434

(Cl. Z55-27) 8 Claims.

My invention relates to jars and has particular reference to a jarring tool which may be employed in connection with the art of drilling deep wells.

In the practice of drilling earth bores, particularly for deep wells such as oil wells, it frequently occurs that the drill string employed for making the bore or the drill bits or other tools employed in the bore may become stuck therein, requiring that such stuck tools be loosened before further drilling operations can be resumed. It is the common practice in this art to employ jarring tools for the purpose of imparting blows directed axially of the bore for the purpose of jarring cr shaking the tools loose to permit their removal from the earth bore or to so loosen the tools as to permit the circulation fluid to wash away the loose cuttings which may have caused the tool to stick in the well.

The importance of maintaining the circulation of the wash fluid or circulation fluid during the jarring operations is readily apparent since once the jarringblows have tended to loosen the stuck tools, the circulation fluid has an opportunity to cut through the compacted cuttings or caved in material and remove them from the bore.

Heretofore the jarring tools which have been employed have consisted essentially of an outer or shell member and an inner or mandrel member telescopically assembled together, the shell member having inwardly directed splines or flanges adapted to engage corresponding outwardly directed radial flanges or radially extending splines to provide hammer and anvil abutments for producing the jarring blow. Such constructions necessarily require considerable radial space to accommodate the required strength of material for the interengageable flanges or splines necessary to produce the heavy tonnage of blow by the tool and hence necessarily restricts the amount of space which is permitted within the mandrel member through which circulation fluid may pass. Furthermore, in order to permit the hammer and anvil abutments to strike each other with the requisite jarring force, such jars usually employ interengaging friction members which will permit the exertion of a predetermined strain in the drill string before the friction members release and allow the abutments to come together and the amount of space within the tool required to house such relatively rugged friction members further restricts the permissible size of the wash pipe opening through the mandrel member.

Another disadvantageous feature of previous jar constructions has been their relative lack of possible adjustment while within the well bore, most of the constructions requiring either the entire removal of the jar from the bore in order to change the setting thereof to vary the strength of blow or requiring such complicated manipulation of the drill string and jar as to make such adjustments difficult, if not substantially impossible.

It is therefore an object of my invention to provide a jar in which the hammer and anvil abutments are so constructed as to permit a wash pipe opening through the jar substantially equal in size to the normal wash pipe opening through a section of drill string or the drill collars commonly employed in boring wells.

Another object of my invention is to provide a jar of the character set forth in which the mandrel member is provided with a plurality of abutment members which extend radially outwardly through radially extending slots formed in and penetrating through the walls of the outer or shell member.

Another object of my invention is to provide a construction as set forth in the preceding paragraph in which a plurality of groups of abutment members are provided upon the mandrel and shell members to thereby distribute the impact forces throughout the length of these members as well as to distribute the impact forces at a plurality of points circumferentially of the members.

Another object of my invention is to provide a jar of the character set forth in which a plurality of separate and independent releasable friction members are employed to hold the mandrel and shell members in their relatively contracted posi-` tions.

Another object of my invention is to provide a jar of the character set forth in which the strength of blow to be exerted by the jar may be selected by merely raising and lowering the drill string.

Another object of my invention is to provide a jar of the character set forth in which a plurality of sets of interengaging abutments are provided and in which each set of abutments has associated therewith interengaging releasable friction members permitting the ready selection of one or more of the sets of friction members to determine the strength of blow to be delivered by the jar.

Another object of my invention is to provide a jar which is especially adapted as a drilling jar,-

that is, one which may be continuously associated with the drill string and preferably adjacent the bit during the normal drilling operations and which provides a wash fluid passage substantially equal in cross section to the fluid passages through the sections of drill string.

Other objects and advantages of my invention will be apparent from a study of the following speclcations, read in connection with the accompanying drawings, wherein Fig. l is an elevational view of a jar constructed in accordance with my invention and illustrated as associated with a drill string such as that normally employed for the drilling of oil wells, the mandrel and shell members being illustrated in their contracted or normal positions;

Fig. 2 is an elevational view similar to Fig. l but illustrating the shell and mandrel members in the positions they assume during the pulling of the strain in the drill string preparatory to jarring;

Fig. 3 is an elevational view similar to Figs. 1` and 2 but illustrating the positions of the mandrel and shell members in their extended position at the instant of impact;

Fig. 4 is an elevational view similar to Figs. l, 2 and 3, and illustrating the partially contracted positions of the shell and mandrel members preparatory to striking another jarring blow;

Fig. 5 is a detail vertical sectional View taken through the jar shown in Figs. 1 to 4 and illustrating the manner of construction of the abutments on the shell and mandrel members;

Fig. 6 is a horizontal cross sectional view taken along line VI-VI of Fig. 5;

Fig. 7 is a detail elevational view of a portion of a modified form of abutment and friction release mechanism which may be employed in the practice of my invention; and

Fig. 8 is a detail perspective view of one of the spring friction members which may be employed with my jar.

Referring to the drawings, I have illustrated my jar as comprising two telescopically assembled members including an outer or shell member I and an inner or mandrel member 2. The outer or shell member I consists essentially of an elongated tubular member, the lower end of which is provided with a suitably threaded box 3, by which the shell member I may be coupled to the pin end 4 of a drill collar or a section of drill pipe with which my jar is associated. The external diameter of the shell member I may be selected of any suitable size, preferably a diameter which is substantially equal to the diameter of the drill collar employed upon the drill string or equal to the maximum diameter of tool joints employed to connect the several sections of the drill pipe together.

The internal bore 5 of the shell member I likewise may be of any suitable selected size, preferably the greatest possible diameter which will leave a shell thickness to the shell member I of suflcient strength to transmit the rotary forces required` to perform the normal drilling operations and to withstand the strains and impacts during the jarring operations.

The mandrel member 2 is provided at its upper end with a suitably threaded pin member 6 adapted to be received in a box 'I of a drill string section disposed immediately above it, the body portion of the mandrel member 2 comprising a tube extending down through and making a sliding t Within the bore 5 of the shell member I. A wash opening 8 extends down through the mandrel member I and is made as large as is permissible to leave a requisite wall thickness suflicient to transmit the rotary forces and to withstand the impact forces, as was described for the shell member I.

By referring to Figs. 1 through 4, it will be observed that the shell member I is provided with a plurality of longitudinally extending slots 9, I0 and II, such slots being formed to extend radially through the entire wall of the shell member I so as to permit the projection therethrough of short splines I2, I3 and I4 formed upon the mandrel member 2. The splines l2, I3 and I4 may be formed as separate pieces of metal secured to the body portion of the mandrel member 2 as by Welding though, for the purpose oi' withstanding the necessarily great impacts to which they will be subjected, I prefer to form these splines integrally with the body portion oi' the mandrel member 2 as by turning a single solid piece of metal having the diameter of the enlarged upper end I5 of the mandrel member (see Fig. 5) to produce the reduced diameter portions I6, I'I and I8 between the splines I2, I3 and I4, and then milling out or otherwise removing the material from the mandrel member 2 circumferentially to leave the splines I2, I3 and I4 as integral portions of the single piece mandrel member 2.

When employing this integral construction of the splines with the body of the mandrel member 2, the shell member may be readily constructed as two complementary semi-cylindrical halves Ia and Ib into which the slots 9 may be cut and then the two halves Ia and Ib may be placed about the mandrel and welded together along the weld lines indicated at I9.

As will be understood from the foregoing description, the width of the slots 9, III and II should be at least as great as the wall thickness of the shell member I while the thickness of the splines I2, I3 and I4 should be suflciently great as to make a relatively close sliding fit within the slots 9, I0 and II. Thus rotary force applied through the drill string to the mandrel member 2 will be transmitted through the interengaging splines and slots to the outer or shell member 2 and thence to the drill sections or drill bit disposed below the shell 2. Also it will be noted that the upper ends 9a, Illa and IIa of the slots 9, I0 and II will constitute anvil abutments against which the upper ends or faces Iza, I3a and I4a of the splines I2, I3 and I4 will strike as hammers when the mandrel section is pulled upwardly relative to the shell section or member 2 to produce the jarring blow.

As will be understood by those skilled in this art, the lowering of the mandrel member in the shell member to the contracted position shown in Figs. 1 and 5 and then a sharp or sudden upward movement imparted to the mandrel member 2 will cause the spline abutments I2a, I3a and I4a to strike a jarring blow upon the shell abutments 9a, Illa and Ila so that with the construction thus far described a reciprocating motion imparted to the drill string will result in a series of jarring blows.

However, it is desirable that the blow which is struck should be one of relatively great force and I therefore prefer to hold the mandrel and shell members in their contracted positions until a predetermined upward strain has been imparted to the upper portions of the drill string and then to suddenly release or free the shell and mandrel members so that the force of the strain taken in the drill string will bring the '15, r I I f abutments of my Jar into sudden and forceful contact with each other. For this purpose I provide friction members to interconnect the mandrel and shell members in their collapsed positions but which will release these members when a predetermined strain has been imposed between them. For example, I provide a friction member 20 associated with the uppermost slot 9, such friction member comprising a short length of suitable metal such as spring steel, one face of which is provided with a laterally extending projection 2| extending completely thereacross, as is illustrated particularly in Fig. 5. The friction member 20 is disposed in a recess 22 formed in the shell member I as an extension of the slot 9, the friction member 20 being held in place within the recess 22 by means of screws 23 which are preferably threaded into the body of the shell member I and are provided with enlarged heads adapted to overlie the friction member 20. I prefer to rabbet the outer face of the friction member 20 throughout its length, as indicated at 24, so as to permit the heads of the screws 23 to set flush with the outer periphery of the shell member I. I also prefer to form the recess 22 with an enlargement or curved portion 25 disposed opposite to the projection 2|.

'I'hus when the mandrel member is drawn upwardly relative to the shell member, the spline Y I2 will engage the projection 2| on the friction spring 20 and further upward movement of the mandrel member will be restrained until sufficient upward force is exerted upon the drill string to overcome the friction between the projection 2| and the spline. At this time the spring friction member 20 will bow away from the slot 9 and permit the spline I2 to pass the projection 2|, such bowing of the spring producing the effect of suddenly releasing the restraint and permitting the spline I2 to be brought into a sharp impact against the abutment 9a of the slot 9.

The form of the invention as illustrated herein contemplates the employment of slots 9 and splines I2 formed on diametrically opposite sides of the jar, as is shown particularly in Figs. and 6, though it will be understood by those skilled in this art that .three or four or more slots and splines corresponding to slots 9 and splines I2 may be employed distributed about the circle described by the shell and mandrel members for the purpose of providing a greater number of friction release devices 20 and a greater number of abutment members to receive the impact. Thus by selecting the number of slots, splines and friction gripping members, the amount of force which will be required to release the friction members, and hence the amount of force which will be exerted by the impact of the abutment members against each other, may be selected at any desired value.

Moreover, by employing a multiplicity of slots and splines I2 and arranging additional groups of slots and splines along the length of my jar, a still greater releasing force may be selected and a still greater impact may be provided. Again it will be noted that by arranging a relatively large number of groups of splines and slots, the impact forces may be distributed throughout the length of the jar as well as about the circumference thereof.

While if desired all of the splines, slots and friction release members on the jar may be made identical with each other, I provide a ready means for variably selecting the strength of blow which will be exerted by providing the friction members 20 associated with one group of splines and slots to be engaged when the mandrel and shell members are contracted but a portion of the total length of travel permitted between these members and providing another group of splines and slots with friction members which will only be engaged when the contracting movement exceeds the distance required to interengage the friction members of the first group of splines and slots, and I may arrange friction members associated with a third or additional groups of splines and slots, each to be engaged only by a contracting travel of the shell and mandrel members progressively additional amounts.

'I'his may be readily accomplished by providing the spring friction members 20a associated with the slot I0 and spline I3 with a limited amount of travel in the direction of the extended or expanded positions of the mandrel and shell members as by forming the recess 22a in which the friction member 20a is mounted of a length in excess of the length of the friction member Thus as the mandrel member is drawn upwardly relative to the shell member, the spline I3 will engage the projection 2Ia on the spring member 20a and thereafter the spring member 20a will move upwardly with the mandrel member until the upper end of the spring member 20a engages the upper limit of the recess 22a. 'I'hen and only then will the spring member 20a exert its restraining force. However, the location of the projection 2|a when the spring member 20a is in its uppermost position should be such that the spring member exerts its restraining force at the same time that the spring memer 20 exerts its restraining effort upon the spline I2 associated with the slot 9. Thus the restraining effort of the spring member 20a is added to the restraining effort of the spring member 20 and hence twice the force will be required to simultaneously release the friction spring members 20 and 20a.

Similarly, the friction spring member 2Gb associated with the spline I4 and slot II may be mounted in a recess 22h of even greater length than the recess 22a so that it may move through a greater distance between its normal or raised position as shown in Fig. l and its gripping or restrained exerting position as shown in Fig. 2. Again, however, it should be noted that the restraining effort should be exerted at the same point of upward travel of the mandrel or extension movement of the mandrel as that point at which the spring members 20 and 20a exert their restraint.

It follows therefore that if the mandrel and shell members are in their normal or completely contracted position as shown in Fig. 1 and a jarring blow is desired, a lifting of the drill string 'I will draw the mandrel 2 upwardly to the position shown in Fig. 2. It will be noted that at this time the friction members 20, 20a and 20h are all positively engaged with their respective splines I2, I 3 and I 4. Exertion of the upward strain necessary to overcome the forces of the friction springs 20, 20a and 20h will cause these springs to flex laterally and suddenly release the mandrel splines, allowing the mandrel to move upwardly with a swift movement until the abutments 9a, I2a, Illa, I3a, Ila and Ida engage and produce the strong upward jarring blow,

Now if the first jarring blow fails to dislodge the tool or other device suspended below my jar, second and additional blows may be given by merely lowering the drill string 'I to move the mandrel member again to its contracted position relative to the shell.

If the maximum strength of blow is again desired, the mandrel and shell members may be moved to their fully contracted positions as shown in Fig. 1. However, if a lesser blow is desired, all that is required is to but partially contract the shell and mandrel members as illustrated in Fig. 4 wherein the mandrel 2 has been moved downwardly relative to the shell member I just a suiiicient distance to dispose the spline I2 below the projection 2| on the friction spring member 20.

By referring to Fig. 3, it will be observed that once the splines have passed the projections on their associated friction springs, the friction springs 20a and 20h will be free to drop downwardly from their uppermost positions as shown in Fig. 2, theamount of such downward movement permitted each of these members being determined by the relative distances between the lower end of the recesses 22a and 22h and the lower ends of the slots and with which they are associated.

Hence during the lowering movement as described, the lower end of the splines I3 and I4 will have engaged the projections 2|a and 2|b of their spring members and will have flexed these members laterally as shown in Fig. 4. However, before the mandrel will have been moved downwardly sufficiently to permit projections 2|a and 2Ib to engage above the splines I3 and I4, the spline I2 will have passed below the projection 2| and its spring member 20. Thus if the lowering movement is stopped at this point and again the drill string is drawn upwardly, only the spring members associated with the splines I2 and slots 5 will have effectively reengaged and the strain which will be required to release these members will be only a portion of the strain required to release all of the spring members 20, 20a and 20h. Thus a blow taken from this partially contracted position will be but a portion of the total possible blow had all of the spring members been reengaged.

Also it will be noted that if a heavier jarring blow, but not the maximum blow, is required the mandrel 2 may be moved downwardly to a second partially contracted position which will permit the splines I3 to engage below the projections 2 I a on the'spring members associated therewith while at the same time the spring members 20 will have engaged above their associated splines |2 but the springs 20h will not have engaged above their splines |4. If now an upward strain is taken on the drill pipe a jarring blow will be given which will be equal to the added effects of all of the springs 20 and all of the springs20a but still not as great as the combined effects of all of the springs 20, 20a and 20h.

Thus an operator can readily select the strength of blow which is to be exerted and may vary this blow at will merely by controlling the amount of lowering movement given to the drill string after each blow.

While the normal position of the mandrel and shell members has been described as the fully contracted position shown in Fig. l, it will be understood by those skilled in this art that the normal position may be the fully extended position shown in Fig. 3 since in ordinary drilling operations the drill string is maintained in tension rather than compression so that the jar may be coupled into the drill string in its extended position and be maintained in such position until a jarring blow is required. Then by merely lowering the drill string to the desired amount, the appropriate jarring blow may be produced.

To facilitate the re-cocking of the jar or the reengagement of the splines below their respective spring friction members, I prefer to provide the projections 2| on the spring members with a gradual sloping surface 2|a: to be engaged by the lower end of the splines during the contracting movement to thus provide for a relatively great wedging action during this movement but I provide a relatively sharp angle face 2|y to be engaged by the upper end of the mandrel splines so as to decrease the wedging action and to produce a more nearly snap action of the spring members only after the relatively great requisite strain has been produced between the splines and springs.

While in Figs. 1 through 5 I have illustrated only a single projection 2| on each of the spring members, it will be apparent that if a greater frictional engagement between the splines and spring members is required, a multiplicity of projections may be formed upon the splines and the spring members as shown particularly in Fig. 7, wherein one side face of the spline |2c is formed with laterally extending projections 30, 3| and 32 adapted to interengage projections 33, 34 and 35 formed upon a spring friction member 2Ic. In this form of the device, the rear face of the spring members 2Ic may be formed with additional projections 36, 31 and 38 and 39 so staggered with reference to the forward projections 33, 34 and 35 as to provide a substantial bridge behind each oi the projections 33, 34 and 35 and thus permit substantially independent deflection of the spring member 2Ic at the rear of each of the projections 33, 34 and 35, In order to permit all of the forward projections on the spring member 2Ic and all of the projections on the spline 9c to interengage at the same time and to permit free release of these projections simultaneously, the side face of the spline 9c may be formed with a downwardly and inwardly sloping taper while the spring member 2|c may have its outer face formed with a corresponding downwardly and outwardly sloping taper. Thus when the spline 9c is raised to interengage the projections 33, 34 and 35 of the spring member 2|c, all of these projections will be simultaneously engaged. When the strain has been imposed sufficient to flex the spring member 2Ic to release the spline |2c, the amount of taper of the projections 3|), 3| and 32 is such that when projection 33 is freed from projection 35 it will pass freely by projections 34 and 33 as the spline is moved upwardly into striking abutment with the upper end of the slot 9c. To provide for the longitudinal movement of the spring member 20c, as described with reference to the slidable spring members 20a and 2017, the rabbeted portion of the spring members 20c may be formed adjacent the ends thereof.

It will be observed therefore that I have provided a jar in which, without sacrifice of strength of either the shell or the mandrel members, I am permitted to provide a relatively great diameter wash opening 8 through the mandrel, through which circulation fluid may pass just as freely as it passes through any of the sections of drill string or through the drill collar with which my jar may be associated. It should be noted, however, that to prevent leakage of the circulation fluid between the mandrel and shell members in either of the contracted or extended positions of my jar, a packed sliding joint should be provided which is illustrated particularly in Fig, 5 as including an enlargement 40 of the bore 8 adjacent the lower end of the mandrel, into which projects a tube or nipple 4| screwed or otherwise secured to the interior of the lower end of the shell member I as indicated at 42. A counterbore 43 at the lower end of the bore 40 may be packed with suitable packing material 44 held in the desired degree of compression by means of a compression ring 45 screwed into the counter bore 43.

While in the foregoing description I have particularly described the features of my new jar which permits the same to be used as a drilling jar during the normal drilling of the well bore, it will be apparent to those skilled in this art that the construction is equally well adapted for use in connection with fishing tools employed to remove broken or stuck tools, pipes and the like i from the well.

While I have shown and described the preferred embodiment of my invention, I do not desire to be limited to any of the details of construction shown or described herein, except as defined in the appended claims.

I claim:

l. In a jar construction, the combination of a shell member and a mandrel member telescopically assembled together for longitudinal movement relative to each other between a contracted and an extended position, a plurality of radially disposed slots formed through the walls of said shell members and elongated in the direction of the longitudinal axis of said shell member, splines formed on said mandrel member and extending radially therefrom through said slots, said splines having a width substantially equal to the width of said slots to prevent relative rotary movement between said shell and said mandrel members and said splines having a length disposed longitudinally of said slots of less than the length of said slots to permit relative longitudinal movement between said mandrel and shell members before abutment of said splines with the ends of said slots may occur; and friction release means associated with each of said slots and extending into said slots to engage said splines when said splines are spaced away from the abutment ends of said slots to hold said splines outl of abutting relation with said ends of said slots until a longitudinal strain is exerted between said mandrel and said shell member sufficient to overcome said friction release means.

2. In a jar construction, the combination of a shell member and a mandrel member telescopically assembled for longitudinal movement relative to each other between a contracted position and an extended position, a plurality of slots formed through the Walls of said shell member, said slots being elongated in the direction of said longitudinal movement between said members and said slots being disposed in spaced relation to each other about the circumference of said shell member, a plurality of splines formed on said mandrel member and extending radially therefrom through said slots, said splines having a length in the direction of said longitudinal movement less than the length of said slots to permit relative longitudinal movement between I said mandrel and shell members before abutment of said splines with the ends of said slots may occur; and friction release means associated with each of said slots and extending into said slots to engage said splines when said splines are spaced away from the abutment ends of said slots to hold said splines out of abutting relation with said ends of said slots until a longitudinal strain is exerted between said mandrel and said shell member sufficient to overcome said friction release means.

3. In a jar construction, the combination of a shell member and a mandrel member telescopically assembled together for longitudinal movement relative to each other between a contracted position and an extended position, a radially disposed slot formed through the wall of said shell member and elongated in the direction of said longitudinal movement, a spline formed on said mandrel member and extending radially therefrom through said slot, said spline having a length in the direction of said longitudinal movement less than the length of said slot to permit relative longitudinal movement between said mandrel and said shell members before the end of said spline may be brought into abutting relation with an abutment end of said slot, and friction release means associated with said slot and extending into said slot to engage said spline when said spline is spaced away from the abutment end of said slot to hold said spline out of abutting relation with said end of said slot until a longitudinal strain is exerted between said mandrel and shell members sufficient to overcome said friction means.

4. In a jar construction, the combination of a shell member and a mandrel member telescopically assembled together for longitudinal movement relative to each other between a contracted position and an extended position, a plurality of radially disposed slots formed through the walls of said shell member, a plurality of splines formed on said mandrel member one for each of said slots and extending radially therefrom through said slots, the length of said splines disposed longitudinally of said slots being less than the longitudinal length of said slots to permit relative longitudinal movement between said mandrel and shell members before the end of each of said splines engages an abutment end of its associated slot, friction means associated with each of said slots for engaging said splines and holding said splines in spaced relation to the abutment ends of said slots until the exertion of a predetermined longitudinal strain between said mandrel and shell members.

5. In a jar construction, the combination of a shell member and a mandrel member telescopically assembled together for longitudinal movement relative to each other between a contracted position and an extended position, a plurality of radially disposed slots formed through the walls of said shell member, a plurality of splines formed on said mandrel member one for each of said slots and extending radially therefrom through said slots, the length of said splines disposed longitudinally of said slots being less than the longitudinal length of said slots to permit relative longitudinal movement between said mandrel and shell members before the end of 6, In a jar construction, the combination of a shell member and a mandrel member telescopically assembled together for longitudinal movement relative to each other between a contracted position and an extended position, a plurality of slots disposed in spaced relation to each other, each of said slots extending radially through the wall of said shell member and being elongated in the direction of the longitudinal movement between said members, a plurality of splines formed upon said shell member and extending radially therefrom through said slots, each of said splines having a length in the direction of said longitudinal movement less than the length of its associated slot, friction means associated with said slots to engage said splines and to hold said splines in spaced relation to an abutment end of said slots until a predetermined longitudinal strain is exerted between said members, said friction means being disposed in said slots to engage said splines when said mandrel and shell members are in a partially contracted position, a second group of slots formed through the walls of said shell member and a second group of splines on said mandrel member extending therethrough, and friction means associated with said second group of slots adapted to engage and restrain said mandrel and shell members from movement to said fully extended position until the exertion of a predetermined longitudinal strain between said members, the friction means associated with said second group of slots being so disposed as to engage their associated splines only when said mandrel and shell members have been contracted to a position further than that required to interengage the friction means associated with said first named group of slots.

7. In a jar construction, the combination of a shell member and a mandrel member telescopically assembled together for longitudinal movement relative to each other between a contracted position and an extended position, a plurality of radially disposed longitudinal slots formed through the walls of said shell member, a plurality of splines formed on said mandrel member, each extending radially therefrom through one of said slots, the length of each of said splines and the length of said slots being such as to pervmit complete travel of said mandrel and shell members between fully contracted position and fully extended position, friction means associated with certain of said slots to engage said splines when said mandrel and shell members are in partially contracted positions and to restrain said members against movement to said extended position until a predetermined longitudinal strain is exerted therebetween, and friction means associated with others of said slots to engage the associated splines to impose a corresponding restraint upon movement of said mandrel and shell members, said last named friction means including means preventing eilective interengagement between them and their associated splines until said mandrel and shell members have been moved to a further contracted position.

8. In a jar construction, the combination 01T a shell member and a mandrel member telescopically assembled for longitudinal movement relative to each other between a contracted position and an extended position, a plurality of radially disposed longitudinal slots formed through the walls of said shell member, a plurality of splines formed on said mandrel member and extending radially therefrom through said slots, the length of said splines and the length of said slots disposed in the direction of longitudinal movement of said members being such as to permit movement of said members between said contracted and extended positions, interengaging means for restraining said shell and mandrel members against movement to said extended position including a plurality of projections formed upon one side of said splines, a recess formed in the side of said slot facing said side of said spline, and a spring member in said recess having a plurality of projections thereon extending toward said spline and interengageable with the projections on said spline, the projections on said spline and said spring means being disposed along a line extending at such angle to the longitudinal axis of said jar that when any one of said spline projections is moved past any one of said spring means projections it cannot reengage with any other of said spring means projections.

JOHN T. PHIPPS. 

